In the field of flat panel display, TFT is a key element for manufacturing a display device. There is a need to continually improve the characteristics of the TFT to achieve a better display quality. One of the research tendencies is to reduce the channel width of the TFT so as to achieve better characteristics. Presently, Single Slit Mask (SSM) is often used to manufacture the TFT channel with a width below 4 μm. FIG. 1 is a structural schematic view showing a conventional TFT channel manufactured by the SSM. As shown in FIG. 1, the TFT channel is provided between a source electrode 1 and a drain electrode 2, and has a U-shaped structure. The U-shaped structure includes a bent portion B and extension portions A provided on both sides of the bent portion B. The channel width at each of the bent portion B and the extension portions A is L. When forming the TFT channel with the width L of 3-3.5 μm, transmittance at the bent portion B may be somewhat reduced compared to that at the extension portions A, decrease of the transmittance may easily occur at the bent portion B of the channel upon performing an exposing process, and accordingly photoresist at this portion may not be removed completely in the following developing process. In this case, short circuit may occur between the source electrode and the drain electrode at the bent portion B after the patterning process is completed.